JPS6271393A - Auto-white balance circuit - Google Patents

Abstract

PURPOSE:To exclude color fading, make a video signal persistent to disturbance, and to simplify the circuit-constitution by detecting the color temperature of the light from a light source in a correction signal generating circuit, executing a closed-loop adjusting action on the video signal based on the result of the said detection thereby to adjust the white balance. CONSTITUTION:When a color temperature detecting circuit 79 outputs a color temperature detection signal that varies in accordance with the color temperature, the amplification factor of an amplifier 77 is adjusted, as well as its offset value is adjusted through a variable resistor 77a, so that a correction signal of such characteristic as coinciding with that of a control value is inputted from the amplifier 77 to a variable gain amplifier 71 of R-signal loop. Similarly, by adjusting the inverse the amplification of an amplifier 78, and adjusting its offset value by a variable resistor 78a, a correction signal of such characteristic as coinciding with that of the control value is inputted from the amplifier to the variable gain amplifier 75 of B-signal loop. In such a way, the white balance is adjusted to approach a target value by closed loop using the signal generated by detecting the color temperature of an actual incident light, therefore, the color fading does not occur even when picking up the image of a mono- colored object and the color balance is properly controlled.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Fields] The present invention is applied to an auto white balance circuit, specifically, a color video camera, an electronic camera, etc., which automatically adjusts the white balance according to the color temperature of the light source. This invention relates to an auto white balance circuit that performs adjustment.

[Prior Art] As is well known, so-called one-touch auto white balance circuits have been widely used as auto white balance circuits applied to imaging devices such as television cameras and electronic cameras. This type of auto white balance circuit obtains a "white base" each time you take a picture by pointing the TV camera at a white subject or by covering the front of the photographic lens with the white cap that comes with the camera. These color differences are adjusted in synchronization with the timing of the setting operation (push button operation) so that the video signal becomes a state corresponding to "white", that is, the two color difference signals R-Y and B-Y. The gain of the signal is automatically adjusted, and the adjusted state is maintained by the storage means until the next push button operation is performed. Therefore, in this method, it is necessary to repeat the setting operation of the photographic shot 1-fi >niho' photo balance, which is cumbersome to handle. Additionally, there is a risk that the photographer may forget the settings and take a picture without maintaining the correct white balance. For this reason, recently, television cameras have been developed that are equipped with a so-called full-auto white balance system circuit that completely automates this white balance operation. An example of a white balance circuit using this method is shown in FIG.

In FIG. 4, the portion surrounded by a dashed dotted line at C is the white balance circuit 10 in the television camera. R from an imaging means (not shown) such as an imaging tube or a solid-state imaging device
The signal RIN is amplified by a variable gain amplifier of 2:11 with a gain set in the same circuit.Then, in the next stage R-Y matrix circuit 12, a low-band luminance signal which is one component of the output of the above-mentioned imaging means is obtained. Y, signal processing is performed, and output as a color difference signal RY. This color difference signal RY output is averaged by an integrating circuit 13 consisting of a resistor R and a capacitor c1, and then inputted to an inverting input terminal of an operational amplifier 14. The non-inverting input terminal of the operational amplifier 14 has a reference voltage VRE.
FI is applied, and the output of the operational amplifier 14 is applied to the variable gain amplifier 11 as its gain setting signal. On the other hand, the B signal BIN from the imaging means is similarly amplified by the variable gain amplifier 15, and then sent to the next stage B-Y matrix circuit 16 as a signal together with the low-band luminance signal YL. The signal is processed and output as a color difference signal B-Y. The color difference signal B-Y is averaged by an integrating circuit 17 including a resistor R and a capacitor C2, and is input to an inverting input terminal of an operational amplifier 18.

The non-inverting input terminal of the operational amplifier 18 has a reference voltage VI? E
F2 is given, and the output of the operational amplifier 18 is given to the variable gain amplifier 15 as its gain setting signal.

The color difference signals R-Y and B-Y, which are the outputs of the white balance circuit 10, are input to the encoder 20, where they are subjected to signal processing such as double-balanced modulation, and are converted into chroma signals (so-called C signals). Output. This C signal is combined in the color multiplexer 3e with the high-frequency luminance signal Yl from the imaging means (and the sync burst signal from a separate oscillation circuit) to form an NTSC composite video signal (color signal).

Here, white balance adjustment in the white balance circuit 10 is performed as follows.

In other words, first of all, in this fully automatic white balance method C, even if the subject is not completely white, the color difference signals obtained corresponding to the subject containing each color on average are the same as the color difference signals obtained corresponding to the white subject. The average value of these color difference signals can be calculated as the color difference signal level obtained when imaging a Japanese or French subject using the light source light at that time. This is based on the assumption that they will be approximately equal. In general, the two color difference signals R-\ and B-Y corresponding to an all-white object under light source light will both be normal if the white balance is properly adjusted (i.e., the signal level will be different from each other). Value ■ ■ RIEFI' RE
F2 becomes equal), and if the adjustment is not appropriate, bias will occur in either the positive or negative direction. White balance circuit 1 shown in Figure 4 above
When the color difference signal level is zero, it operates to make the bias in the color difference signal level zero. For example, if the color temperature of the light source changes to become higher at a certain point, the level of the B signal BIN from the imaging means will double and the level of the R signal RIN will decrease. Then, the level of the color difference signal B-Y rises, and the level of the color difference signal R-
The level of Y changes in the direction of decreasing, and in response to this change, each operational amplifier 18.14 outputs the average value of the changing level through each integrating circuit 17.13.
the signals input to rise and fall, respectively. As a result, each operational amplifier 18.14 operates in the direction of decreasing and increasing the gain of each corresponding variable gain amplifier 11.15, respectively, and as a result, the level of each color difference signal B-Y, R-Y is adjusted to the respective base level. is kept at the academic value (i.e. B-¥-0
．． RY-0).

As described above, the white balance circuit 10 of the above method assumes that even if the subject is not completely white, the average value of the color difference signals corresponding to the subject including each color should be zero. Therefore, the adjustment operation is performed in the same way as when imaging an all-white object. Therefore, closed-loop control is performed on the two color difference signals without particularly detecting the seven color qualities of the light source light. A circuit has already been proposed in which a digital method is applied to the above-mentioned auto white balance circuit to perform more accurate white balance adjustment (see Japanese Patent Laid-Open Publication No. 16916/1983).

On the other hand, an auto white balance circuit that actually detects the color temperature of the light source and fully automatically adjusts the white balance based on this has also been proposed (for example, Japanese Patent Laid-Open No. 56-4993 (see publication). Such an auto white balance circuit is constructed as shown in FIG. In FIG. 5, the milky white filter 4
1 is provided on the front surface, and the light-receiving probe 42 reacts to the R component.
A light receiver 4 consisting of a light receiving element 43 that responds to the OJ and B components.
, preamplifiers 45.46 for logarithmically compressing the outputs of the respective light receiving elements 42.43, and these preamplifiers 45.4.
A color temperature detection circuit 40 having an arithmetic circuit 47 that obtains an output corresponding to the color temperature of the light incident on the light receiver 44 based on each output of 6 is provided independently of the imaging means (not shown). It is being

Based on the color temperature information detected by this circuit 40, the color balance adjustment circuit 50 generates adjustment signals r corresponding to the gains of the R signal system variable gain amplifier 61 and the B signal system variable gain amplifier 62, respectively. The adjustment signal controls the recording gain and adjusts the white balance.

[Problems to be Solved by the Invention] In the conventional circuit explained with reference to FIG. However, problems occur because the white balance adjustment operation is performed without actually detecting the color temperature of the light source. In other words, as mentioned above, this method works even when the subject is not completely white.
Usually, it is based on the assumption that the subject exhibits various colors, and that if you average them, the result will be equivalent to white. Therefore, when an object of a single primary color (for example, a board whose entire surface is red) is imaged, the color moves toward white, resulting in fading.

This is because the circuit shown in Figure 4 above essentially cannot distinguish between changes in the R and B signals caused by color temperature and changes in the R and B signals caused by changes in the color of the subject. be.

Furthermore, in the conventional circuit explained with reference to FIG.
The problem that occurs in the circuit shown in the figure does not occur. However, in this type of auto white balance circuit, the color/! It is necessary to provide the detection means once, which complicates the configuration, and also makes it difficult to design the exterior of the camera depending on, for example, where on the video camera the color temperature detection means is to be placed. Furthermore, gain control of each video signal system is performed without detecting the levels of the color signal R2B or the color difference signals R-Y, B-Y (collectively referred to as video signals). That is, since only interloop control is performed on the video signal, there is a problem that it is vulnerable to disturbances.

The present invention has been made in view of the above-mentioned points, and provides an auto white balance circuit that does not cause fading even when photographing monochromatic objects, is resistant to external disturbances, and has a simple configuration. The purpose is to provide.

[Means and effects for solving the problems] The auto white balance circuit of the present invention includes a first variable gain amplifier that amplifies a signal related to first color information (for example, an R signal) from an imaging means, and a second variable gain amplifier for amplifying a signal relating to second color information (e.g. a B signal) from the means;
A first video signal (e.g. R-Y signal) obtained from the output side of the first variable gain amplifier and a second video signal (e.g. B-Y signal) obtained from the output side of the second variable gain amplifier.
A correction signal corresponding to the color temperature of the light incident on the imaging means is generated based on the above-mentioned Y signal), and this correction signal is used to adjust the if of the first variable gain amplifier and/or the second variable gain amplifier. ! The color temperature of the light source is detected by the detection signal generation circuit, and the video signal is closed loop based on this detected value. By performing the adjustment operation, it acts to adjust the white balance.

[Embodiment] FIG. 1 is a block diagram of an auto white balance circuit showing an embodiment of the present invention. The R signal R1,1 from the imaging means (not shown) is amplified by the first variable gain amplifier 71 with a gain set by the output of the amplifier 77 as described later, and then sent to the next stage R-Y matrix circuit. At 72, a low-range luminance signal YL, which is one component of the output of the imaging means, is detected.
The signals are combined with each other, subjected to signal processing, and output as a color difference signal RY. This color difference signal R-Y is integrated and averaged by an integrating circuit 73 consisting of a resistor R3 and a capacitor C3, and the color temperature detection circuit ? 9 will be powered by humans. Similarly, the B signal BIN from the imaging means is amplified by the second variable gain amplifier 75 with a gain set by the output of the inverting amplifier 78 as will be described later, and is then amplified by the next stage B-Y. In the matrix circuit 76, signal processing is performed together with the low-band luminance signal YL, and the signal is output as a color difference signal B-Y.

The color signal B-Y is integrated and averaged by an integrating circuit 74 consisting of a resistor R and a capacitor C4, and is input to a color temperature detection low path 79. The other ends of capacitors C3 and 04 are grounded. Resistor RR and capacitor C of integrating circuits 73 and 74
The values of 3 and C4 are set to 3'4 R3-R4, C3-C4.

The color temperature detection circuit 79 calculates the ratio f (B-Y) / (R-Y) l from the color difference signals R-Y and B-Y, and sends this to the amplifier 77 as a DC color temperature detection signal. Leads to 78. The value of the color temperature detection signal ((B-Y)/(R-Y)l, which is the ratio of the color difference signals R-Y and B-Y, changes as shown in Figure 2 as the color temperature changes. Then, this color temperature detection signal i (B-
Y) / (R-Y)I is appropriately amplified with the same polarity by the jH4 amplifier 77, and this amplified color temperature detection signal is sent to the first ITJ variable gain amplifier 71 for controlling the gain of the R signal. It is manually input as a correction signal. In addition, the color temperature detection signal f (RY) / (RY) +
is inverted and amplified by the inverting amplifier 78, and this inverted and amplified signal is sent to the second variable gain amplifier 75.
(It is manually inputted as a correction signal for controlling the gain of the signal.) In this way, the color temperature detection circuit 79 and
A closed loop of the R signal system is formed by the positive signal generation circuit, and the color temperature detection circuit 79 and the amplifier 7
A closed loop of the B signal system is formed by the correction signal generation circuit consisting of 8. In each of the amplifiers 77 and 78, the offset value of each closed loop can be adjusted by offset variable resistors 77a and 78a. The auto white balance R-Y. B-Y is input to an encoder 20 (see FIG. 4) and subjected to signal processing.

On the other hand, the white balance control target value on the camera side in response to changes in color temperature (the control value for reproducing the white of the subject as white on the television receiver in response to changes in color temperature) is as shown in Figure 3. , R signals are expressed by the characteristics of the control value V2, and the B signal is expressed by the characteristics of the control value VB. Therefore, when the color temperature detection circuit 79 outputs a color temperature detection signal that changes with respect to the color temperature ' as shown in FIG. 2, the amplifier 77 adjusts its amplification factor and the offset value by the variable resistor 77a. By doing so, the variable gain amplifier 71 of the R signal system is changed from the amplifier 77.
By manually inputting a correction signal with characteristics matching the characteristics of the control value (2), and similarly adjusting the amplification factor of the inverting amplifier 78 and the offset value by the variable resistor 78a, the B signal from the amplifier 78 is A correction signal having characteristics matching the characteristics of the control value VB is input to the variable gain amplifier 75 of the system. By doing this, the white balance adjustment will be performed in an open loop to approach the target value using the signal that detects the color temperature of the actual incident light, so there will be no fading even when imaging a single primary color subject. , appropriate color balance control can be performed.

Furthermore, as a basic characteristic of the feedback loop, it is clear that even if a disturbance is applied to each closed loop of the R1B system, the disturbance will be suppressed to 1/loop gain. In other words,
Information about color temperature is + (B-Y)/ (R-Y)l
The fact that the above-mentioned closed loops are formed to control the gains of the R and B signals is due to the change in color temperature of I(B-Y)/(
Even if a change in RY)l is added to each of the closed loops as a disturbance, the amplifier 77 is affected by each of the R and B closed loops.
．． By matching the characteristics of the correction signal from 78 with the white balance control target value, stable full-auto white balance adjustment can be achieved without the influence of such disturbances.

In the above embodiment, the color temperature detection circuit 79 detects the color temperature of the illumination light by taking the ratio of the color difference signals R-Y and B-Y, or it detects the color temperature of the illumination light by taking the ratio of the color difference signals R and B.
(B/R), or the calculated value floε+ (B-'I-) - (R
-Y)l-] may be used to detect the color temperature.

[Effects of the Invention] As described above, according to the present invention, the white balance is adjusted in accordance with the color temperature of the light incident on the imaging means, so there is no fading even when imaging a single primary color object, and the variable gain can be adjusted. Since the gain control of the amplifier is performed in a closed loop, it is resistant to external disturbances (1111) and has excellent effects such as simple configuration.

[Brief explanation of drawings]

Fig. 1 is a block diagram of an auto white balance circuit showing an embodiment of the present invention, Fig. 2 is an output characteristic diagram of the color temperature detection circuit of the auto white balance circuit shown in Fig. 1 above, and Fig. 3 is a line diagram showing the white balance control target value on the camera side with respect to color temperature, Fig. 4 is a block diagram showing an example of a conventional auto white balance circuit, and Fig. 5 is a diagram showing an example of a conventional auto white balance circuit. It is a block diagram showing an example. 70...Auto white balance circuit 7
1...First variable gain amplifier 75...
...Second variable gain amplifier) So□No Strategy 1 Strategy 2Z Strategy 3 Senku Utsukuri

Claims (1)

[Claims] A first device that amplifies a signal related to first color information from an imaging means.
a second variable gain amplifier that amplifies a signal related to second color information from the imaging means; a first video signal obtained from the output side of the first variable gain amplifier; A correction signal corresponding to the color temperature of the light incident on the imaging means is generated based on a second video signal obtained from the output side of the second variable gain amplifier, and this correction signal causes the first variable gain amplifier to and/or a correction signal generation circuit for controlling the gain of the second variable gain amplifier.